This invention relates to tufting machines and more particularly to a drive for driving the tufting instrumentalities in a tufting machine at very high speeds.
In the art of tufting one or more rows of yarn carrying needles are reciprocably driven through a base material fed through the machine to form loops that are seized by loopers or hooks oscillating below the base material in timed relationship with the needles.
The needles are typically mounted in a needle bar supported at the end of a plurality of push rods constrained for reciprocatory motion toward and away from the loopers or hooks. In those machines having a sliding needle bar arrangement, i.e., wherein the needle bar is controllably driven by pattern means transverse to the direction of movement of the backing material a needle bar carrier supports the needle bar, the carrier being secured to the push rod and moving therewith and permitting the needle bar to reciprocate with the push rods yet slide relatively to the push rods.
Conventionally reciprocating motion of the push rods have been effected by various types of drives generally of two types, namely an eccentric cam mounted on a rotation shaft and connected to the push rods through an eccentric strap and connecting means, or the push rods have been driven by a linkage arrangement connected to a rock shaft which in turn is driven by a lever connected to an eccentrically mounted circular cam. An example of the former construction is illustrated in Ingram et al. U.S. Pat. No. 3,964,407, and an example of the latter is illustrated in Cobble U.S. Pat. No. 2,977,905, and in numerous other of the patented art. The loopers or hooks and in the case of cut pile machines, the knives, are also driven from mechanism such as sprockets mounted on the end of the main shaft and drivingly connected to the looper or hook and knife rock shafts mounted in the bed of the tufting machine. In such prior art drives all of the tufting instrumentalities are driven directly off the main shaft.
The speed of tufting machines have been increased substantially as the tufting art has gradually developed. As the speeds increase above 1000 rpm those machines of the linkage driven type having levers and rocker arms tend to wear more rapidly, and additionally, because of the lever arms used there is a large tortional moment exerted on the rocker shaft especially at the top and bottom of the stroke. The oscillating movements of the levers in such linkage machines are more difficult to balance than a rotating system utilizing an eccentric cam drive. However, one problem that arises with cam drives is the presence of unbalanced forces that are associated with the larger cams. The unbalanced forces require the use of counterbalancing weights, which, in turn, increase the amount of rotating mass in the drive line placing excessive stress on machine parts and limiting the speed of the machine. Consequently, in both types of drives used in single shaft tufting machines the speeds have been limited.
One approach to this problem is that illustrated in Ingram U S. Pat. No. 4,515,096 which illustrates a counterbalancing system in an eccentric cam driven machine. There additional eccentrics mounted 180.degree. out of phase with the eccentrics which drive the push rods are mounted on a common shaft. Although this approach not only balanced the rotating and oscillating systems, it also balanced the needle reciprocation system.
Another approach, which is illustrated in Scott et al. U.S. Pat. No. 3,839,972, was to utilize an adjustable crank shaft in which the crank and connecting rods that drive the push rods could be positioned relatively to the axis of the crank shaft. Balancing of the rotating system was attained by utilizing counter-weights at ends of the stub shafts to counterbalance the eccentricity of the crank. In linkage driven systems, a counterbalancing rocker shaft is included within the head of the machine and includes additional slotted levers driven by eccentric cams out of phase with the needle drive eccentric cams. Thus, with the exception of Ingram U.S. Pat. No. 4,515,096 only the rotating and oscillating system was balanced, and not the needle reciprocation system.
A proposal was previously made to mount the push rods and eccentric crank drives therefor on a separate shaft and drive that shaft by timing chains or belts from the mainshaft, the latter being driven by the tufting machine motor. In another recent proposal a number of stub shafts each mounting an eccentric thereon and driving a separate push rod was mounted in the head of the tufting machine with each stub shaft being driven by belts from the mainshaft. In these approaches the mainshaft and the shaft or shafts which drive the push rods rotate in the same direction. Any counterbalancing of the reciprocating system has to be accomplished in a manner similar to that disclosed in Ingram U.S. Pat. No. 4,515,096, i.e., mounting weights on the push rod driving shaft. However, the mounting of additional weights on the push rod driving shafts increases the mass of the push rod system and places excessive forces on the bearings. In the proposal utilizing separate stub shafts for each push rod, the stub shafts effectively are cantilevered and additional weight on the stub shaft would excessively load the bearings.
In view of the need to have tufting machines operate at the highest possible speeds the load on the needle bar/push rod drive system must be minimized so as to reduce the inertia problems, while counterbalancing the entire system against excessive dynamic forces, including the torsional forces.